I've received a few PMs asking for info on Hydrospan and how it works so I decided to do this small info/tutorial on it. Hope those interested find it useful.

Hydrospan is a 2 part casting substance made by Industrial Polymers Inc. Basically when the casting solidifies (becomes gelatinous) you place it in water and the casting will slowly start to expand (become larger) when it absorbs water.

2. Pour 2 parts of Hydrospan A into one of the cups (preferably a measuring cup if you have one).

3. Pour 1 part of Hydrospan B into another cup (again preferably a measuring cup so that you can see that the quantity is only 50% of part A but you can eyeball it if you don't have a measuring cup).

4. Mix part A and part B into a third cup using the mixing stick. Mix for about 20 seconds.

5. Pour the mixed Hydrospan into the mold you made. Once mixed you get about 3-4 minutes to pour it in before it gets too thick to pour (the company claims 10 minutes but I didn't get that much time).

6. Allow about 24 hours for the Hydrospan to cure and solidify.

7. Once cured, remove the Hydrospan casting from mold (see pic 2).

8. Place the Hydrospan casting in the 4th cup filled with water (see pic 3). The casting will get noticeably bigger in about 3 hours and will become more than twice as big in 24 hours (the company claims only a 60% increase and wait time of a few days but I got a significantly greater increase and in a shorter amount of time). You can remove the casting from the water to stop the expansion at any time if you want it to be smaller than the maximum size.

9. Remove the expanded Hydrospan casting and let it air dry. It may be deformed in some areas (some areas, depending on thickness, absorbs water more quickly therefore expand faster and larger than other areas) but don't become alarmed (I initially thought this product sucked because the expanded object looked deformed). Once the casting is allowed to air dry for a couple of hours and the excess water is allowed to evaporate the object reshapes itself to be proportional to the original object.

10. The Hydrospanned object is gelatinous so you can't use it as is. Also, if you let it sit long enough all the water will eventually evaporate and it'll go back to it's original size. So, you will need to make a mold of the Hydrospanned object.

11. Make a casting of the Hydrospanned object and voila (see pic 4). If you want an even bigger object you can make a casting from the mold of the bigger object using Hydrospan and allow that to enlarge in water. In theory, you can keep doing this forever (you can make a scout size head be life size!)

There you have it. This stuff is great and you can buy a quart for less than $20.

Disclaimer: Remember to read the precautions and warnings on the label. Wear gloves and a mask and work in a well ventilated area.